UNITIES OF LIFE 



of the protists that the morphological unity is bound up 

 with the physiological. In the case of the histona, 

 the multicellular, tissue-forming organisms, this is only 

 so at the beginning of individual existence (at the 

 stage of the stem-cell). As soon as the multicellular 

 body arises from this cytula by repeated segmentation, it 

 is raised to the stage of a higher individuality, the cell- 

 state. 



Our own human frame is, in its mature condition, like 

 that of all the higher animals, a very complete cell-state, 

 but a single cell at the beginning of its existence. We 

 speak of the life-unity of the former as an actual bion, 

 and that of the latter as a virtual bion; in other words, 

 the physiological individual or the life-unity has in the 

 first case reached the highest stage of individual develop- 

 ment that pertains to its species, while in the second 

 case it remains at the lowest stage of virtual formation, 

 and has only the capacity of rising to the higher stage. 

 In the higher plants and animals only one cell of the 

 organism, or the two combined sexual cells (ovum and 

 spermium), are the potential bion which may develop 

 into an actual one. There are, however, exceptions. In 

 the fresh-water polyp (hydra) and cognate cnidaria each 

 piece of the body-wall, in the bath-sponge (euspongia) 

 and similar sponges each piece of tissue, and in many 

 plants (for instance, marchantia among the crytogams 

 and bryophyllum among the phanerogams) each portion 

 of a branch or leaf, has the power to develop into a 

 mature organism; and is, therefore, a virtual bion. 



From these virtual bionta (parts of the body that may 

 grow into whole organisms) we must distinguish the 

 partial bionta which have not this property. These are 

 separated parts of the body that live for a time after 

 being cut off from the whole organism, but then die off. 

 Thus, for instance, the heart of a tortoise beats for a 

 long time after being cut out. A flower that has been 



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